Protest adds to tensions before presidential run-off amidst anger over acquittal of top officers in Mubarak trial.

CAIRO - Activists urged Egyptians to turn out for a big protest on Tuesday to reclaim a revolt they say has been hijacked after Hosni Mubarak was jailed for life but top security officials freed in a trial seen as a sign his old guard remain in charge.

Although Mubarak was imprisoned on Saturday over the killing of protesters, he escaped the death penalty and senior officers tried with him were acquitted for lack of evidence so many now believe the ex-president could win with an appeal.

The calls to hit the streets, almost 16 months after Mubarak was toppled, have also been fueled by a looming June 16-17 presidential run-off vote between Mubarak's last prime minister and a conservative Islamist, a choice that has polarized Egypt.

Many Egyptians who voted for centrist candidates in last month's first round now face a wrenching choice between Mohamed Mursi of the Muslim Brotherhood, which already controls parliament, and Ahmed Shafiq, an ex-military man like Mubarak.

"No to Mursi, no to Shafiq, the revolution is half way through," read a placard held up by one youth in Cairo's Tahrir Square, calling for a boycott of the vote. Hundreds were already in the square on Tuesday morning.

The vote is the final step before the army which took charge when Mubarak was driven out formally hands over to a new president by July 1, formally ending a transition marred by protests, political bickering and sometimes bloodshed.

But divisions on the street have become more pronounced in the final countdown. While thousands demonstrated in Tahrir late on Monday, some wanted a boycott of the vote and others argued with Islamists over whether or not to back Mursi.

The April 6 movement and liberal or centrist parties or groups, in their demands for Tuesday's rally, said they wanted the presidential vote put on hold till a law is passed to block Shafiq, a senior member of Mubarak's government, from running.

Rights

The Muslim Brotherhood, with a chance to secure Egypt's top job after decades of repression by Mubarak, said it would join the protest but has not called for any election delay.

Instead, its demands focus on a retrial for those it accuses of killing protesters, a trial for Shafiq who was appointed premier while anti-Mubarak demonstrations were still going on, and a rejection of any bid to "reproduce the previous regime."

"We came to get our rights and the rights of the martyrs, and we don't want Ahmed Shafiq," said Hussein Ahmed, 30, one of those in Tahrir on Tuesday.

Protesters in the square could all agree that Shafiq, branded one of the "feloul" or remnants of Mubarak's era, should be kept out of power. But they were divided about whether or not Mursi is, as he has told voters, a revolutionary candidate.

Many distrust the Brotherhood for reneging on an earlier pledge not to run for the presidency and say it has sought to hog power since it won the biggest bloc of seats in parliament, winning many more seats that it originally said it would seek.

Talks between Mursi and two losing candidates, leftist Hamdeen Sabahy and ex-Brotherhood member Abdel Moneim Abol Fotouh who came third and fourth in last month's first round vote, have yet to yield an explicit endorsement for Mursi.

Sabahy and Abol Fotouh have declared the election void because of alleged violations and have pushed for the formation of a presidential council - a body likely to include them.

The Brotherhood has said such a council would be unconstitutional but Mursi said he would be willing to appoint vice presidents from outside the group.

The votes secured by Abol Fotouh and Sabahy make up about 40 percent of those cast in the first round and could be vital to a Mursi win.

Shafiq's supporters have kept a lower profile. Many of his voters come from among Egyptians who were happy to see the back of Mubarak but are now desperate to see law and order reinstated and the economy put back on its feet.

They include liberals and Christians who fear an Islamist leader will trample on social freedoms and build an Islamic state. Mursi insists people will be free in their opinions and in what they wear under his rule.

One campaigner for Shafiq said his supporters would rally in their cars in a Cairo district to show their backing for Shafiq, who supporters see as having the army's backing to deliver on his pledge to restore order.

Although the generals will formally hand over power by July 1, analysts and diplomats expect them to remain an influential player from behind the scenes for years to come.